Electrolyte electroreflectance study of TiO₂ films modified with metal nanoparticles

Abstract

Electrolyte electroreflectance (EER) has been used as an in situ probe for determining the distribution of energy states at the surface of naked and metal-modified TiO 2 film in contact with aqueous solution. The surface modification of polycrystalline TiO 2 films by electrodeposition of fine (a few nanometers in size) metal particles has been shown to result in the appearance of surface states with an energy of approximately 2.15 eV for Cu, 2.40 eV for Pd, 2.50 and 2.30 eV (two peaks in the EER spectrum) for Pt, and 2.65 eV for Ag (the energy values are measured versus valence band edge of TiO 2 ). The important role of metal-induced surface states in the enhancement of charge exchange between conduction band of semiconductor oxide and metal islets has been demonstrated using the electrocatalytic oxidation of boron hydride as a model reaction.

Investigation of nanostructured TiO2 surface and interface electric fields with photoreflectance spectroscopy

“…Their values and feature assignment agrees well with the 368 ± 1.4 kJ/mol (3.811 ± 0.015 eV) direct gap of anatase TiO 2 determined using thermoreflectance . On the other hand, Kulak et al obtained ER spectra for 100 nm films of amorphous (300°C annealing), anatase (450°C annealing), and mixed anatase‐rutile (700°C annealing) TiO 2 prepared by hydrolysis of poly(butyl titrate). Annealing induced an intense signal in the sub‐bandgap range of 230–290 kJ/mol (2.4–3.0 eV); the prominent spectral feature was attributed to localized surface and grain boundary electronic states.…”

Determination of the Energy Levels of Paramagnetic Centers in the Band Gap of Nanostructured Oxide Semiconductors Using EPR Spectroscopy

“…TiO 2 , MoO 3 , WO 3 , etc.) is very sensitive to the structure of energy levels arising in their band gap as the result of bulk doping and surface modification. − These energy levels are responsible for intraband optical transitions and govern the recombination of the photogenerated charge carriers as well as their involvement into the interfacial reactions. − The elucidation of the exact position of energy levels which could be involved in the charge transfer reactions and photoelectron trapping is of fundamental importance for the investigations of photocatalytic behavior of TiO 2 , MoO 3 , V 2 O 5 and their nanoheterostructures which are able to accumulate the photoiduced charges and to generate the reactive oxygen species for a long-term activity after illumination. − …”

“…For the evaluation of energy levels created as the result of doping of a semiconductor matrix or modification of its surface, several experimental techniques were employed including photoluminescence, , a photo-Hall effect, impedance and electrolyte electroreflectance, ,, spectroscopic ellipsometry, and diffuse optical reflectance . These methods where used for bare, metal, and N-doped TiO 2 as well as for some other nanostructured semiconductors.…”

“…25−29 Besides this, in the case of mixed nanoheterogeneous oxide semiconductors with wide band gap, e.g., TiO 2 /MoO 3 or TiO 2 /V 2 O 5 , the injection of photogenerated electrons from TiO 2 to the MoO 3 or V 2 O 5 nanoparticles results in spatial separation of electrons from holes, which prevents their fast recombination after switching off the illumination. 13,14 For the evaluation of energy levels created as the result of doping of a semiconductor matrix or modification of its surface, several experimental techniques were employed including photoluminescence, 30,31 a photo-Hall effect, 32 impedance and electrolyte electroreflectance, 8,33,34 spectroscopic ellipsometry, 35 and diffuse optical reflectance. 36 These methods where used for bare, metal, and N-doped TiO 2 as well as for some other nanostructured semiconductors.…”

A novel electrochemical device for the disinfection of fluids by OH radicals

“…1 eV below the conduction band edge which facilitate electron transfer into the conduction band. 1,2 However, hole conduction has also been reported in HfO 2 and TiO 2 , 3 and hence it was postulated that a hole current may be induced via injection from the Si to the TiO 2 surface, and that this would be facilitated by rendering the metal overlayer on the TiO 2 negative. By fabricating the metal overlayer in the form of a grid, holes may be generated at the open surface of the TiO 2 and such carriers may be available for reactions in an external fluid.…”